The invention is directed to a method for determining a characteristic curve of a clutch of a clutch activation system in a drivetrain, in particular of a motor vehicle, in which the clutch is activated by an actuator, wherein a bite point of the clutch is adapted as a first reference point of the characteristic curve.
DE 10 2010 024 942 A1 discloses a method for controlling a dual clutch transmission with at least two sub drivetrains, of which each can be coupled to an internal combustion engine by means of a clutch. While the motor vehicle comprising the dual clutch transmission is in drive mode, a bite point of the clutch is determined independently of the engine torque. The bite point constitutes a support point of the clutch characteristic curve for this.
With a motor vehicle with a hybrid drivetrain, the drive resistance can be overcome by two independent energy sources, in most cases the fuel of an internal combustion engine and electrical energy from a traction battery of an electric motor, by conversion into mechanical energy. According to DE 10 2008 030 473 A1, a vehicle with P2 hybrid topology is known, in which the electric motor is disposed at a second point in series with the internal combustion engine. Between the two components a separating clutch that is disposed immediately after the internal combustion engine can enable a purely electric drive in the disengaged state or can pass torque from the internal combustion engine to the drive wheel in the engaged state.
A further function of the separating clutch consists of starting the internal combustion engine. For this purpose, energy is transferred to the static internal combustion engine by a targeted increase of the torque of the electric motor and engaging the separating clutch, and said engine is thus accelerated. Regarding the ride comfort, the torque transferred by the separating clutch must be precisely known during this in order to avoid unintended acceleration of the vehicle, because the torque of the electric motor is also transferred to the drive wheels at the same time.
The torque transferred by the separating clutch is directly dependent on the position of the clutch activating actuator. For estimating the transferred clutch torque, on the one hand the position of the actuator relative to the possible travel must be known, on the other hand the clutch characteristic curve (clutch torque as a function of the actuator position) must be referenced to the actuator travel.
A stop on the left or right end of the disengagement travel is approached for referencing the position of the actuator that activates the separating clutch. This referencing is mainly carried out following a long period with the vehicle at a standstill in order to check the position of the actuator on the travel path.
The clutch characteristic curve is not constant due to different influencing factors such as wear, readjustment of the clutch, temperature and ageing processes. The bite point is referenced for ensuring the accuracy of the clutch torque during a restart of the internal combustion engine. In order to accurately determine the characteristic curve on the actuator axis, with the internal combustion engine at a standstill, a bite point is adapted by slowly engaging the separating clutch and analyzing the influence of the engaging clutch on the electric motor, which is rotated at a predetermined revolution rate. In doing so, due to a predetermined target clutch torque only a negligible torque is transferred by means of the separating clutch. The bite point is determined by analyzing a signal response from the electric motor that can be associated with the target clutch torque.
Furthermore, the position of the preload point is required in order to impose a constant axial preload on the release bearing during the hybrid mode. A method for operating an activating device of a clutch with a stator device, a rotor device that can be rotated relative to the stator device and a carriage device with a release element that can be displaced relative to the rotor device in the axial direction to a limited extent, which can be brought into contact with a disk spring of the clutch, is known from DE 10 2013 205 109 A1. For this a preload point is determined such that the release bearing of the carriage device exerts a minimal pressing force on the disk spring of the clutch during rotation of the clutch, wherein the stator device is energized to displace the carriage device such that the preload point is not exceeded during rotation of the clutch. For determining the preload point, the stator device is energized such that the carriage device is displaced in the axial direction into a region in which the preload point is assumed to lie, and the current drain of the stator device and/or the revolution rate of the rotor device and/or the speed of the carriage device in said region are monitored.
The adaptation of the bite point of the clutch and the preload point of the actuator to the clutch can only be carried out independently of each other and only in certain cases.